Facebook Flickr Last.fm (Does that count? It's probably the one I use the most, being a music fiend). Tumblr (Don't think that counts at all...but maybe).
I have a MySpace account, but I don't really use it.
Oh, I belong to Club of Mars, but I always forget to go poke around there.
I do have pages on myspace, livejournal and ning, but they are hardly ever checked anymore.
Facebook i dislike almost as much as myspace these days. Not really in to playing in to memes or excessive applications, as they add unnecessary clutter to what is essentially supposed to be a giant rolodex. Myspace i find to be really cluttered and full of spam. Livejournal i don't frequent much anymore just because i stopped journalling to myself and decided i actually wanted to talk to people and do something about my goals, not just let them stagnate. Ning... i have an account there, but really haven't done much with it. way too many communities within communities. too much to keep track of.
The point not being for us to discuss stuff (we do that here), but to get charts and see what we're all listening to. I'll post this somewhere else I'm sure.